GN: Replace mojo/system.gni with forwarding groups

mojo/examples/wm_flow/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
-import("//mojo/system.gni")
 
 assert(use_aura)
 
 group("wm_flow" ) {
   deps = [
     ":app",
     ":embedded",
     ":init",
     ":wm_flow_wm",
   ]
 }
 
 # GYP version: mojo/mojo_examples.gypi:mojo_wm_flow_wm
 shared_library("wm_flow_wm") {
   output_name = "mojo_wm_flow_wm"
 
   sources = [
     "wm/wm.cc",
   ]
 
   deps = [
     "//base",
     "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/services/public/cpp/view_manager",
     "//mojo/services/window_manager:lib",
-  ] + mojo_system_for_shared_library
+  ]
 }
 
 # GYP version: mojo/mojo_examples.gypi:mojo_wm_flow_init
 shared_library("init") {
   output_name = "mojo_wm_flow_init"
 
   sources = [
     "init/init.cc",
   ]
 
   deps = [
     "//base",
     "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/services/public/interfaces/view_manager",
-  ] + mojo_system_for_shared_library
+  ]
 }
 
 # GYP version: mojo/mojo_examples.gypi:mojo_wm_flow_app
 shared_library("app") {
   output_name = "mojo_wm_flow_app"
 
   sources = [
     "app/app.cc",
   ]
 
   deps = [
     ":embedder_bindings",
     ":embeddee_bindings",
     "//base",
     "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/services/public/cpp/view_manager",
     "//mojo/services/window_manager:lib",
-  ] + mojo_system_for_shared_library
+  ]
 }
 
 # GYP version: mojo/mojo_examples.gypi:mojo_wm_flow_embedded
 shared_library("embedded") {
   output_name = "mojo_wm_flow_embedded"
 
   sources = [
     "embedded/embedded.cc",
   ]
 
   deps = [
     ":embedder_bindings",
     ":embeddee_bindings",
     "//base",
     "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
     "//mojo/services/public/cpp/view_manager",
     "//mojo/services/window_manager:lib",
-  ] + mojo_system_for_shared_library
+  ]
 }
 
 # GYP version: mojo/mojo_examples.gypi:mojo_wm_flow_embedder_bindings
 mojom("embedder_bindings") {
   sources = [
     "app/embedder.mojom",
   ]
 }
 
 # GYP version: mojo/mojo_examples.gypi:mojo_wm_flow_embeddee_bindings
 mojom("embeddee_bindings") {
   sources = [
     "embedded/embeddee.mojom",
   ]
 }